Frequency detector and control voltage supply



seem-62m L. M. HERSHEY Filed Nov. 1:5, 1940 FREQUENCY DETECTOR AND. CONTROL VOLTAGE SUPPLY o tut-4124 March 17, 1942.

INVENTOR LLOYD HERSHEY ATTORNEY -ceived signal intensities.

Patented Mar. 17, 1942 UNITED STATES PATENT OFFICE FREQUENCY DETECTOR AND. CONTROL VOLTAGE SUPPLY Lloyd M. Hershey, Great Neck, N. Y., assignor to Hazeltlne Co po ation, a c p ation of Delaware Application November 13, 1940, Serial No. 365,442

11 Claims.

The present invention relates to an improved carrier-signal frequency detector and controlvoltage supply system and, particularly, to such a system for detecting a frequency-modulated carrier signal and simultaneously deriving from the carrier signal a control voltage which is particularly suited for use as an automatic amplification control bias, tuning indicator control bias, or the like. J

It is frequently desirable, from the standpoint of simplicity and economy, to provide a frequency-modulated carrier-signal receiver which does not require an amplitude-limiting system, the function of which is to remove undesirable amplitude modulation from a received carrier signal. The amplitude-limiting system of such a receiver has heretofore frequently been used additionally .to'supply an automatic amplification control bias by which the signal input to the detector of the receiver is maintained within a' relatively narrow range for a wide range of re- In the event that the limiting system .is omitted from the receiver, it becomes necessary to find another source of automatic amplification control bias. The conventional frequency detector included in such a re-- ceiv er comprises means for developing a unidirectional voltage across each of two load impedances, one of which voltages is of .proper polarity to provide an automatic amplification control bias. However, this voltage is unsatisfactory forautomatic amplification control purposes since the magnitude of the bias varies continuously with the mean frequency of the carrier signal over the frequency-response range of the de- 3 tector, the voltage having minimum and maximum amplitudes at opposite ends of the frequency-response range. Thus, when this voltage b used to control the amplification of the receiver, the amplification varies considerably with detuning and the maximum audible output is obtained when the receiver is badly detuned from the desired carrier signal. v

An automatic amplification control bias has been'obtained in accordance with one prior art arrangement by designing the primary circuit of the detector frequency-responsive network with a relatively high impedance. A rectifier device and load impedance are coupled across this circuit to derive across the load impedance by rectification of the carrier signal an automatic amplification control bias. This arrangement has the serious disadvantage that the high-impedance primary circuit renders it diilicult to obtain a linear output characteristic for the frequency 60 detector and there is, consequently, material distortion of the modulation components of the carrier signal.

It is frequently convenient to use the automatic amplification control bias also to control a tuning indicator device preferably provided in the carrier-signal receiver as an aid in tuning the receiver exactly to a desired carrier signal. Consequently, it is desirable that this bias be obtained from the output of the detector frequency-responsive network in order that thereceiver shall be so tuned that the carrier signal applied to the detector has a mean frequency correspondingto the mid-frequency of the frequency-response range of the detector. Furthermore, from the standpoint of accurate tuning indications, it is desirable that the control bias have an amplitude characteristic with a change of slope at the mid-frequency-of the detector response range. While a control bias derived in accordance with the aforementioned prior art arrangement, comprising a high-impedance primary circuit having a rectifier device and load impedance coupled thereto, may have this type of amplitude characteristic, the control bias is not normally satisfactory for tuning indication purposes since the change of slope of the characteristic doesnot necessarily occur exactly at the mid-frequency of the detector response range and, in fact, does" not ordinarily occur at the mid-frequency if the detector is designed for a carefully balanced output. Such control bias is also unsatisfactory from the standpoint that it is not derived from the output of the detector frequency-responsive network. f

It is an object of the present invention, therefore, to provide a new and improved combined carrier-signal frequency detector and controlvoltage supply which avoids one or more of the disadvantages and limitations of the prior art devices.

It is a further object of the invention to prorectification of a received carrier signal two unidirectional control voltages having over a predetermined range of frequency deviation of thecarrier signal similar amplitude characteristics but opposite polarities.

It is an additional object of the inventionto detector and control-voltage supply comprises a frequency-selective network including two sections having predetermined frequency-response characteristics of the same type but sloping in opposite senses with frequency over a predetermined range of frequency deviation of a carrier signal applied thereto. The system includes a modulation-signal detector including a pair of rectifier devices individually coupled to the network sections, each of the devices having anindividual load impedance across which there is developed by rectification of the carrier signal a unidirectional modulation voltage. There is also provided a control-voltage supply circuit including an additional rectifier device and a load impedance coupled to one of the network sections to derive by rectification of the carrier signal a unidirectional voltage, and an output circuit for cumulatively combining the last-named derived voltage anda unidirectional voltage derived from the other of the network sections to provide a unidirectional control voltage.

In accordance with a particular form of the invention, a carrier-signal control-voltage supply comprises a frequency-selective network including two sections having predetermined frequency-responsive characteristics of the same type but sloping in opposite senses with frequency over a predetermined range of frequency deviation of a carrier signal applied thereto. There is included a pair of rectifierdevices individually coupled to the sections and means including a load impedance common to the rectifier devices for developing across the impedance byrectification of the applied carrier signal a unidirectional control voltagehaving an amplitude minimum at the mid-frequency and amplitude maxima near the end frequency of the aforesaid range of frequency deviations.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Referring now to the drawing, Fig. 1 is a cir cuit diagram, partly schematic, of a complete frequency-modulated carrier-signal receiver of the superheterodyne type embodying the invention; Fig. 2 is a graph comprising curves representing the output of the frequency-responsive network of the frequency detector and the output of the control-voltage supply of the Fig; 1 arrangement; Figs-3 and 5 are circuit diagrams of modified forms of the invention; and Fig. 4 is a graph comprising curves showing voltage relations at certain points in the arrangement of Fig. 3.

Referring now more particularly to Fig. 1,

there is represented schematically a complete frequency-modulated carrier-signal receiver of a conventional design embodying the present invention in a preferred form. In general, the receiver includes a radio-frequency amplifier l0 having its input circuit connected to an antenna system H, l2, and having its output circuit con nected to an oscillator-modulator l3. Connected in cascade with the oscillator-modulator 13, in the order named, are an intermediate-frequency amplifier I4 of one or more stages, a combined carrier-signal frequency detector and controltomatic amplification control or A. V. C. circuit is connected between the output of the controlvoltage supply of unit l5 and the input circuits of one or more of the tubes of the radio-frequency amplifier Hi, the oscillator-modulator l3, and the intermediate-frequency amplifier M, in conventional manner.

It will be understood that the various units just described may, with the exception of the carriersignal frequency detector and control-voltage supply I5, be of conventional construction and operation, the details of which are well known in the art, rendering detailed description thereof unnecessary. Considering briefly the operation of the receiver as a whole, and neglecting for the moment the operation of the frequency detector and control-voltage supply l5 presently to be described, a desired frequency-modulated carrier signal is selected and amplified by the radiofrequency amplifier I0, converted to a frequencymodulated intermediate-frequency carrier signal in the oscillator-modulator l3, amplified in the intermediate-frequency amplifier l4, and detected by the frequency, detector of unit l5, thereby to derive thea'udio-frequency modulation components. The audio-frequency components are. in turn, amplified in the audio-frequency amplifier l6 and are reproduced by the sound reproducer I! in a conventional manner. A control voltage derived by the control-voltage supply of unit l5'is used as an automatic amplification control of A. V. C. bias and is effective to control the amplification of one or more of the units l0, l3, and M to maintain the signal input to the detector of unit I5 within a relatively narrow range for awide range of received signal intensities.

Referring now more particularly to the portion of the system embodying the present invention,.

there is coupled to the intermediate-frequency amplifier l6 a frequency-responsive network It! including two sections I9, 20. The network I8 includes a primary circuit of relatively low impedance comprising windings 2| and 22 coupled respectively to the network sections l9 and 20. The network sections l9 and 20 are individually tuned on opposite sides of the mid-frequency and -near the end frequencies of the normal range of frequency deviation of the carrier signal to be 21, 28 and the load resistor 8| have a common terminal. Unidirectional modulation voltages are developed across the load impedances 21, 28 by rectification of the carrier signal and are combined with opposing polarities and. applied to the input circuit of the audio-frequency amplifier l6. An output circuit comprising a filter including a series resistor 88 and shunt condenser 84 cumulatively combines unidirectional voltages derived across the load impedances 28 and 8| to provide a unidirectional control voltage and applies this voltage as an automatic amplification control bias through a conductor designated as A. V. C. to the input circuits of one or more of the tubes of units l8, l8, and l4.

In considering the operation of the circuit just nal applied from amplifier I4 to the network |8.'

The frequency detector 24 rectifies the carrier signal to derive across the load impedances 21, 28 the modulation components thereof. These modulation components are applied to the audiofrequency amplifier l8 for amplification and eventual reproduction by the sound reproducer The carrier signal developed across the network section l8 also is rectified by the rectifier device 88 to derive across load impedance 8| a unidirectional voltage which is cumulatively combined by the'A. V. C. circuit with that derived across load impedance 28 to derive a negative unidirectional control voltage having an amplitude characteristic representedby curve 0 of Fig. 2. It will be seen that the amplitude of this voltage is substantially constant over the frequency range f, h, which is greater than the normal range of frequency deviation of the carrier signal, as is desirable for automatic amplification control purposes.

Fig. 3 is a circuit diagram of a modified form ofthe invention essentially similar to the arrangement of Fig. 1, similar circuit elements the load impedances 21, 28. The carrier signal is rectified by rectifier devices 88, 85 to derive across load impedance 8| a negative unidirectional control voltage and across load impedance 88 a positive unidirectional control voltage. The curves of Fig. 4 represent the magnitudes of these unidirectional voltages with variations of frequency of the intermediate-frequency carrier signal. It will be evident that each of these unidirectional control voltages has an amplitude minimum at the mid-frequency f0 and amplitude maxima near the end frequencies f, h of the range of frequency deviation of the applied carrier signal. Curve e shows the magnitude of the voltage derived across the load impedance 8| and curve d that derived across load impedance 88. The former unidirectional voltage is suitable for use as an automatic amplification control bias while the latter voltage may be used, for example, as a control bias forthe tuning indicator device 48, the change of slope of its of each of curves a1 and b1.

characteristic at the mid-range frequency 10 furnishing an accurate indication when the receiver is accurately tuned to a desired carrier signal. The broken-line curves a1 and b1 extendedinto individual portions of curve d correspond to the curves a and b of Fig. 2 and represent, as before, the individual frequency-response characteristics of the network portions l8 and 28. It will thus be evident that the amplitude characteristic of the unidirectional voltages developed across the load impedances 8| and 88 correspond to portions arrangement of the load impedances 8| and 88 in common to the rectifier devices 88 and 85. As

thus arranged, the voltage derived across one or both of the load impedances by that one of the rectifier devices to which the larger amplitude values of carrier signal is applied, when the mean frequency of the carrier signal departs from the frequency in, is sufficiently large to reduce the operativeness of the other rectifier device or, should the mean frequency of the carrier signal depart suiliciently far from the frequency being designated by similar reference characters,

except that the control-voltage supply system 28 includes an additional rectifier device 85 coupled through a condenser 88 to the network section 28 of the frequency-responsive. network l8 and includes an additional load impedance 88 common to the two rectifier devices 88, 85. As thus arranged, the rectifier devices 88, 85 are individually coupled through the common series load impedance 88 to the network sections I8, 28. Means is provided for connecting the seriesrelated load impedances 8| and 88 in shunt to the rectifier devices 88 and 85 comprising a center-tapped resistor 81 connected between corresponding elements of thelatter rectifier devices. A second output circuit, comprising a filter including a series resistor 89 and a shunt condenser 48 applies the unidirectional potential derived across the load impedance 88 to a .tuning indicator device 48.

The operation of this modified form of the invention is essentially similar to that of the Fig. l arrangement. As in Fig. 1, the modulation components of the carrier signal are derived across 10, even to render the other rectifier device erative. I

If the impedance of the load impedance 88 is reduced to zero, a unidirectional voltage having the amplitude characteristic represented by curve e of Fig. 4 is still derived across the load impedance 8|; On the other hand, if the load impedance 8! has a zero value of impedance, a positive unidirectional voltage having an amplitude characteristic, represented by curve 11, of

inop- Fig. 4 is developed across the load impedance 88.

Obviously, by adjusting the values of the load impedances 8| and 88 any desired intermediate magnitudes of control voltages may be procured. Thus, the arrangement of Fig. 3 is capable of deriving two unidirectional voltages of opposite polarities, the magnitude of one or both of the unidirectional-voltages being controllable.

Fig. 5 is a circuit diagram representing an additional modified form of the invention which is essentially similar to the arrangement of Fig. 1, similar circuit elements being designated by simi-' lar reference characters, except that an additiona1 rectifier device 4| is individually coupled through a condenser 42 to the network section 28. The rectifier device 4| has a load impedance 48 across which there is developed a unidirectional voltage by. rectification of a carrier signal applied to network l8. In this modification, the coupling of the rectifier device 88 to the network section I9 is completed through the condenser 82 This is due to the in the output circuit comprising elements 33 and 34 that the voltages derived across those load z impedances are cumulatively combined to pro-" vide a unidirectional control voltage. This means comprises an isolating impedance 45 interposed between rectifier devices 30 and 41 to isolate the individual circuits of the rectifier devices for carrier signals while permitting the unidirectional voltages derived across the load resistors 3| and 43 to be cumulatively combined in an output circuit comprising a filter network including the series resistor 33 and the shunt condenser 34.

The operation of this modified form of the invention is essentially similar to that of the Fig. 1 arrangement and will not be repeated, the unidirectional control voltages derived across the load impedances 3 I, 43 and applied to the outputcircuit filter network 33, 34 having the amplitude characteristic represented by curve of Fig. 2.

From the above description of the invention, it will be evident that the impedances 21, 28 and 3| of Fig. l, the impedances 21, 28, 3| and 38 of Fig. 3, and the impedances 21, 28, 3| and 43 of Fig. 5 in each instance comprise an impedance network including a plurality of impedance branches. The several rectifier devices of each figure comprise a plurality of rectifier devices for individually coupling these impedance branches to determined ones of the network sections 19, 20 of the frequency-selective network l8. A first output circuit is coupled to the impedance branches 21, 28 to derive a modulation voltage the magnitude and polarity of which vary .with the frequency of the carrier signal applied to unit in opposite senses from the mid-frequency in of the range of frequency deviation of the applied carrier signal. A second output circuit, comprising in Figs. 1, 2 and 3 the elements 33, 34 and additionally in Fig. 2 the alternative or additional output circuit elements 39, 40, is coupled to'the impedance branches of the impedance network to derive a unidirectional control voltage having an amplitude minimum at the mid-frequency f0 and amplitude maxima near the limiting frequencies 1', ii of the range of carrier-signal frequency deviation.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

. 1. A combined carrier-signal frequency detecthaving an individual load impedance across which there is devolped by rectification of said carrier signal a unidirectional modulation volt-' age, and a control-voltage supply circuit includ- 'ing an additional rectifier device and a load im-- pedance coupled to one of said sections to derive by rectification of said carrier signal a unidirectional voltage, and an output circuit for cumulatively combining said last-named derived voltage and a unidirectional voltage derived from the other of said .sections to provide a unidirectional control voltage.

2. A combined carrier-signal frequency .detecttor and control-voltage supply comprising, a frequency-selective network including two sections having predetermined frequency-response characteristics of the same type but sloping in opposite senses with frequency over a predetermined range of frequency deviation of a carrier signal applied thereto, a modulation-signal detector including \a pair of rectifier devices individually coupled to said sections, each of said devices having a serially-connected individual load impedance across which there is developed by rectification of said carrier'signal a unidirectional modulation voltage, and a control-voltage supply circuit includingan additional rectifier device and a load impedance connected in shunt thereto coupled to one of said network sections to derive by rectification of said carrier signal a unidirectional voltage, and an output circuit for cumulatively combining said last-named detector including a pair of rectifier devices indiput circuit for cumulatively combining the voltages derived across one of said impedances and said resistor to provide a unidirectional control voltage.

4.A combined carrier-signal frequency detector and control-voltage supply comprising, a frequency-selective network including two sections having predetermined frequency-response characteristics of the same type but sloping in opposite senses with frequency over a predetermined range of frequency deviation of a carrier signal applied thereto, a modulation-signal detector including a pair of rectifier devices individually coupled to said sections, each of said devices having an individual load impedance across which there is developed by rectification of said carrier signal a unidirectional modulation voltage, and a control-voltage supply circuit including an additional rectifier device and shuntconnected 'load resistor coupled to one of said,

sections to derive by rectification of said carrier signal a unidirectional voltage, said load impedances and said lead resistor all having'a common terminal, and an output circuit for cumulatively combining the voltages derived across one of said impedances and said resistor to pro vide a unidirectional control voltage. 5.-A combined carrier-signal frequency detector and control-voltage supply comprising, a

frequency-selective network including two sections having predetermined frequency-response characteristics of the same type but sloping in opposite senses with frequency over a predetermined range of frequency deviation of a carrier signal applied thereto, a modulation-signal detee-tor including a pair of rectifier devices individually coupled to said sections, each of said devices having an individual load impedance across which there is developed by rectification of said carrier signal a unidirectional modulation voltage, and a control-voltage supply circuit including an additional pair of rectifier devices individually coupled to saidnetwork sec-' tions, each of said last-named devices having an individual load impedance across which there is derived by rectification of said carrier signal aunidirectional voltage, an output circuit, and means for so connecting said last-named'load impedances in said output circuit that said lastnamed derived voltages are cumulatively combined to provide a unidirectional control voltage.

6. A combined carrier-signal frequency detector and control-voltage supply comprising, a frequency-selective network including two sections having predetermined frequency-response characteristics of the same type but sloping in opposit senses with frequency over a predetermined range of frequency deviation of a carrier signal applied thereto, a modulation-signal ,de-

' tector including a pair of rectifier devices individually coupled to said sections, each of said devices having an individual load impedance across which there is developed by rectificationfi ofs'aid carrier signal a unidirectional modulation voltage, and a control-voltage suppl circuit including an additional pair of rectifier devices individually coupled to said network sections, each of said last-named devices having an individual load impedance across which there is derived by rectification of said carrier signal a unidirectional voltage, an output circuit, and an isolating impedance interposed between said lastnamed devices for so connecting said last-named load impedances in said output circuit that said last-named derived voltages are cumulatively combined to provide a unidirectional control voltage.

7. Acarrier-signai control-voltage supply comprising, a frequency-selective network including two sections having predetermined frequencyresponse characteristics of the same type butsloping in opposite senses with frequency over a predetermined range of frequency deviation of a carrier signal'applied' thereto, a pair of rectifier devices individually coupled to said sections, and means including a load impedance common to a said rectifier devices for developing across said impedance by rectification of said applied carrier signal a unidirectional control voltage having an amplitude minimum at the mid-frequencyand amplitude maxima near the end frequencies of said range of frequency deviation.

8. A carrier-signal control-voltage supply comprising, a frequency-selective network including two sections having predetermined frequencyresponse characteristics of the same type but a predetermined range of frequency deviation of a carrier signal applied thereto, and a pair of rectifierv devices individually coupled through a. common load impedance to said sections to derive across said load impedance by rectification of said carrier signal a unidirectional control voltage having an amplitude minimum at the mid-frequency and amplitude maxima near the end frequencies of said range of frequency deviation.

9. A carrier-signal control-voltage supplywcomprising, a frequency-selective network including .two sections having predetermined frequency response characteristics of the same type but sloping in opposite senses with frequency over a predetermined range of frequency deviation of a carrier signal applied thereto, a pair of rectifier devices individually coupled to. said sections, and a load impedance common to said rectifier devices and connected in shunt thereto to derive by rectification of said carrier signal a unidirectional control voltage having an amplitude minimum at the mid-frequency and amplitude maxima near, the end frequencies of said range of frequency deviation.

10. A carrier-signal control-voltage supply comprising, a frequency-selective network including two sections having predetermined frequency-response characteristics of the same type but sloping in oppositesenses with frequency over a predetermined range of frequency deviation of a carrier signal applied thereto, a pair of rectifier devices individually coupled to said sections, arload impedance common to said devices and connected in shunt thereto for deriving by rectification of said carrier signal a first control voltage, and a load impedance common to said devices and connected serially therewith for deriving by rectification of said carrier signal a second control voltage having polarity opposite to that of said first control voltage.

11. A combined carrier-signal frequency detector and control-voltage supply comprising, a

frequency-selective network including two sections having predetermined frequency-response characteristics of the same type but sloping in opposite senses with frequency over a predetermined range of frequency deviation of a carrier signal applied thereto, an impedance net-.

work including a plurality of impedance branches, a' plurality of rectifier devices for individually coupling said branches to predetermined ones of said network sections to develop unidirectional voltages across said branches by rectification of said carrier signal, a first output circuit coupledto saidimpedance branches to derive a modulation voltage the magnitude and polarity of which vary with the frequency of said carrier signal in opposite senses from the mid-frequency of said range of frequency deviation, and a second 1 out-put circuit coupled to said impedance branches to derive a unidirectional control voltage having an amplitude minsloping in opposite senses with frequency over I ima near the limiting frequencies of said range of frequency deviation;

LLOYD M. HERSHEY. 

